Since 1965, the Applicant has been studying the endocrine events underlying the onset of maternal behavior in the puerperal rat. The present proposal is also concerned with maternal behavior, but not with its onset. Rather, interest is now focused on the mechanisms that serve to maintain the behavior once it is established and serve, in addition, to synchronize it to the changing nurtural demands and response attainments of a growing litter. Additionally, there is the attempt to study maternal behavior in a situation less restrictive than the cage, that is, in a situation in which mother and young are free to withdraw from each other and in which species members of all ages and both sexes are represented.